The ACE acts on converting angiotensin-I to angiotensin-II. Angiotensin-II increases blood pressure and is considered a main cause of essential hypertension. A variety of studies have been directed to substances inhibiting ACE actions, whereby to suppress blood pressure rise.
Therapeutic vasodepressors such as Captopril and D-2-methyl-3-mercaptopropanoyl-L-proline have been synthesized as ACE inhibitors. From foodstuff, peptides having ACE inhibiting activities have been separated through enzymatic hydrolysis of casein [Japanese Laid-Open Patent Publication Nos. 62-270533, 64-5497, 64-83096] and soybean protein[Japanese Laid-Open Patent Publication Nos. 3-1671981].
Synthetic ACE inhibitors exhibit strong activities, however, they have adverse effects in many cases and generally are not considered safe. ACE inhibitory Peptides derived from casein or soybean protein have been developed with expectation of low toxicity and high safety, even though they exhibit low activities. Recent studies, therefore, have been focused on separating ACE inhibitors from foodstuff materials and manufacturing them on a large scale by chemical synthetic methods.
An ACE inhibitor derived from food protein was first reported in 1979 by Oshima et al [Oshima, G., Shimabukuro, H. and Nagasawa, K.: Peptide inhibitors of angiotensin-I converting enzyme in digests of gelatin by bacterial collagenase. Biochim. Biophys. Acta., 556. 128(1979)].
Oshima et al obtained 9 peptides consisting of 3 to 12 amino acid residues by hydrolyzing gelatin for 24 hours with collagenase from Clostridium histolyricum. Of those, 6 peptides having alanine-hydroxyproline at their C-terminal end exhibit relatively high ACE inhibiting activities(IC.sub.50 =8.3-37 .mu.M), while those having proline-X at the C-terminal end exhibit relatively low ACE inhibiting activities(IC.sub.50 =123.4-146.5 .mu.M).
Since then over 40 ACE inhibitory Peptides have been disclosed to date [Ariyoshi, Y.: Angiotensin converting enzyme inhibitors derived from food proteins. Trend in Food Science & Technol., May, 139(1993)].
From enzymatic hydrolysate of milk casein, a peptide having a amino acid sequence of phenylalanine-phenylalanine-valine-alanine-proline-phenylalanine-proline-g lutamic acid-valine-phenylalanine-glycine-lycine corresponding to 23-34 residues of .alpha.-casein B, a pentapeptide of phenylalanine-phenylalanine-valine-alanine-proline(IC.sub.50 =6.0 .mu.M) [Maruyama, S. and Suzuki, H.: A peptide inhibitor of angiotensin-I converting enzyme in the tryptic hydrolysate of casein. Agric, Biol. Chem., 46(5), 1393(1982)] and a heptapeptide of alanine-valine-proline-tyrosine-proline-glutamine-arginine, an equivalent of 177-183 residues of .beta.-casein [Maruyama, S. Nakagomi, K., Tomizuka, N. and Suzuki, H.: Angiotensin-I converting enzyme inhibitor derived from an enzymatic hydrolysate of casein. II. Isolation and bradykinin potentiating activity on the uterus and the ileum of rats. Agric. Biol. Chem., 49(5), 1405(1985)] have been identified as ACE inhibitors. Based on the pentapeptide of phenylalariine-phenylalanine-valine-alanine-proline, a series of peptides with different amino acid sequences have been synthesized; valine-alanine-proline, phenylalanine-valine-alanine-proline, phenylalanine-alanine-proline with ACE inhibiting activities similar to that of parent pentapeptides[Kohmura, M., Nio, N. and Aryoshi, Y.: Inhibition of angiotensin converting enzyme by synthetic peptide fragments of various .beta.-caseins. Agric. Biol, Chem., 54(4), 1101(1990)].
In enzymatic .alpha.-zein hydrolysate, three more ACE inhibitory peptides such as leucine-arginine-proline were reported [Miyoshi, S., Kaneko, T., Ishizawa, Y., Fukui, F., Tanaka, H. and Maruyama, S.: Structures and activity of angiotensin converting enzyme inhibitors in .alpha.-zein hydrolysate. Agric. Biol. Chem., 55(5), 1221(1991): Miyoshi, S., Kaneko, T., Ishizawa, Y., Fukui, F., Tanaka, H. and Maruyama, S.: Hypertensive activity of enzymatic .alpha.-zein hydrolysate. Agric. Biol. Chem., 55(5), 1407(1991)].
Other ACE inhibitory peptides have been derived from foodstuff such as sour milk [Nakamura, Y. Yamamoto, N., Sakai, K., Okubo, A., Yamazaki, S. and Takano, T.: Purification and characterization of angiotensin-I converting enzyme inhibitors from sour milk. J. Dairy Sci., 78, 777(1995)], tuna tissue [Kohama, Y., Matsumoto, S., Oka, H., Teramoto, T., Okabe, M. and Mimura, T.: Isolation of angiotensin converting enzyme inhibitor from tuna muscle. Biochem. Biophys. Res. Comm., 155(1), 332(1988)], sardine muscle [Matsuda, H., Ishizaki, T., Moritam H., Nagaoka, T., Osajima, K. and Osajima, N.: Digestion of peptides from sardine muscle that inhibit angiotensin-I converting enzyme by intestinal enzyme of pigs. Nippon Nogeigaku Kaishi, 66(11), 1645(1992)], oyster protein [Matsumoto, K., Ogikubo, A., Yoshino, T., Matsui, T. and Osajima, Y.: Separation and purification of angiotensin-I converting enzyme inhibitory peptides in peptic hydrolyzate of oyster. Nippon Shokuhin Kogyo Gakkaishi, 41(9), 589(1994)], Ficus carica [Maruyama, S., Miyosh, S. and Tanaka, H.: Angiotensin-I converting enzyme inhibitors derived from Ficus carica. Agric. Biol. Chem., 53(10), 2763(1989)], rice [Muramoto, M., Kawamora, Y., Rice protein and anti-hypertensive peptides derived from rice protein. Food Ind. 34(11), 18(1991)], sake and its by products [Saito, Y., Nakamura, K., Kawato, A., and Imayasu, S.: Angiotensin-I converting enzyme inhibitor in sake and its by-product. Nippon Nogeigaku Kaishi, 66(7)], etc.
Furthermore, numerous patent applications have been filed in relation with ACE inhibitory peptides from tri- to nona-: U.S. Pat. Nos. 5449661, 5071955, 4692459, 4585758, 4512979, 4191753, 3832337; EP174162; Japanese Laid-Open Patent Publication Nos. 8-225593, 8-099994, 6-340692, 6-298794, 6-279491, 6-279490, 6-277091, 6-277090, 6-277089, 6-256387, 6-220088, 6-184191, 6-166697, 6-107686, 6-049096, 6-016568, 5-306296, 5-306295, 5-294844, 5-262790, 5-097798, 5-001095, 4-341193, 4-300894, 4-282398, 4-279597, 4-264096, 4-264095, 4-247100, 4-247099, 4-247098, 4-169598, 3-063295, 3-011097.